The present invention relates to a light-amount-adjustment apparatus, a so-called aperture-stop apparatus or the like, to be used in optical apparatuses such as cameras and interchangeable lenses.
Such light-amount-adjustment apparatuses are required to operate with high speed and smoothness. Japanese Patent Laid-Open No. 2-114246 discloses a conventional light-amount-adjustment apparatus (aperture-stop apparatus) shown in FIGS. 12 to 14, which rotates a driving ring around a fixed aperture to rotate plural stop blades as light-blocking blades in open and close directions and thereby changes the size (diameter) of a variable aperture formed by the plural stop blades to adjust the amount of light. This aperture-stop apparatus is also called an iris-aperture-stop apparatus.
As shown in FIGS. 12 and 13, each of the stop blades 210 is provided with a driving pin 211 and a cam pin 212 that protrude from a blade face in opposite directions from each other. The driving ring 220 shown in FIGS. 12 and 14 is formed with plural driving-hole portions 223 with which the driving pins 211 of the stop blades 210 respectively engage.
A base plate 250 shown in FIG. 12 is provided with the fixed aperture 254 that is formed in its central part and plural cam-groove portions 251 that are formed around the fixed aperture 254 and with which the cam pins 212 of the stop blades 210 respectively engage. A retainer plate 240 is disposed so as to sandwich the stop blades 210 and the driving ring 220 with the base plate 250, and is fixed to the base plate 250.
Thus, in the conventional aperture-stop apparatus, the stop blades 210 are rotatably supported in a sandwiched manner between the fixed base plate 250 and the rotatable driving ring 220. Specifically, as shown in FIG. 15, a driving-ring-side blade face, which is an opposite-side blade face to a base-plate-side blade face, of each stop blade 210 is supported by the driving ring 220 shown as a hatched member. On the other hand, of the base-plate-side blade face of each stop blade 210, a reverse portion to the driving pin 211 is supported by the base plate 250.
In addition, of the base-plate-side blade face of each stop blade 210, an area around a reverse portion to the cam pins 212 is supported by blade-supporting portions 228 formed in the driving ring 220 so as to extend outward in a radial direction of the driving ring 220. The blade-supporting portion 228 is provided in the driving ring 220 at plural circumferential places near the driving-hole portions 223. As shown in FIG. 14, a connection portion 211 is formed in circumferential interval portions between the blade-supporting portions 228 so as to circumferentially extend to form a single continuous flange with the blade-supporting portions 228. Base-plate-side faces (that is, stop-blade-side faces) of the blade-supporting portions 228 and the connection portion 221 are formed so as to form a single plane (flange plane).
Moreover, on an inner circumferential side of the driving ring 220, a radial supporting portion 226 is formed so as to have a cylindrical shape and protrude toward the retainer plate 240. At plural circumferential places on an outer circumferential face of the radial supporting portion 226, protrusions 227 are formed, each of which makes contact with an inner circumferential face of the retainer plate 240 so as to allow rotation of the driving ring 220.
As described above, in the conventional aperture-stop apparatus, the opposite-side blade face to the base-plate-side blade face of the stop blade 210 is supported by the driving ring 220 that is a rotatable member, which forms a configuration that causes the rotating stop blade 210 and the rotating driving ring 220 to slide with respect to each other. Such a configuration may increase frictional resistance between the stop blade 210 and the driving ring 220, depending on the relationship of rotational directions of the driving ring 220 and the stop blade 210, which makes it difficult to rotate the stop blade 210 smoothly.
Moreover, of the base-plate-side blade face of the stop blade 210, the area around the reverse portion to the cam pin 212 is supported by the blade-supporting portion 228 of the driving ring 220. However, of the base-plate-side blade face, the reverse portion to the cam pin 212 is not supported, which may cause disengagement of the cam pin 212 from the cam-groove portion 251.
Furthermore, of the driving-ring-side blade face of each of the stop blades 210, an area around the driving pin 211 is supported by the flange plane as a single plane of the driving ring 220. However, such a supporting configuration requires an extremely high flatness of the flange plane in order to reliably support all the stop blades 210. A low flatness of the flange plane may cause fluttering of the stop blades 210 or interference between the stop blades 210 adjacent to each other.
In addition thereto, the single continuous flange formed by the plural blade-supporting portions 228 and the connection portion 221 in the driving ring 220 increases rotational inertia of the driving ring 220, which makes it difficult to drive the aperture-stop apparatus with high speed.
Moreover, the single continuous flange increases radial-directional rigidity of the driving ring 220, which may, if the accuracy of the gaps between the protrusions 227 formed in the radial supporting portions 226 of the driving ring 220 and the inner circumferential face of the retainer plate 240 is significantly high, increase the frictional resistance therebetween or cause excessive radial backlash of the driving ring 220 to cause a deterioration of the control accuracy of the open and close positions of the stop blades 210 (that is, control accuracy of the aperture diameter).